Environmental friendly technology in a vehicle is core technology for survival of a future automobile industry and automakers devote all their energy to developing an environmental friendly automobile for getting over environmental and fuel efficiency regulations.
Examples of future automobile technologies may include an electric vehicle (EV) using electric energy, a hybrid electric vehicle (HEV), and a double clutch transmission (DCT) of which efficiency and convenience are improved.
Particularly, the hybrid electric vehicle using two or more power sources may have various types of combinations, and in general, a hybrid of a gasoline engine or a diesel engine using existing fossil fuel and a motor/generator driven by the electric energy is provided.
The hybrid electric vehicle generally uses an engine and a motor/generator, and uses the motor/generator having a relatively better low-speed torque characteristic as a main power source in a low speed and uses the engine having a relatively better high-speed torque characteristic as the main power source in a high speed.
Therefore, since the hybrid electric vehicle stops an operation of the engine using fossil fuel and uses the motor/generator in a low-speed section, the hybrid electric vehicle has an excellent effect in improvement of fuel efficiency and reduction of exhaust gas.
Further, a transmission system for the hybrid electric vehicle as described above is classified into a single mode type and a multi-mode type.
The single mode type may not require connection units, such as a clutch and a brake for transmission control, but may have the reduced fuel efficiency at the time of high-speed driving and require an additional torque multiplication apparatus so as to apply to a large vehicle.
The multi-mode type may have increased efficiency at the time of high-speed driving and may be designed to enable torque multiplication, thereby being applied to a medium-large size vehicle.
Recently, the multi-mode type is mainly used rather than using the single mode type. Therefore, a research for the multi-mode type has been actively conducted.
The transmission system in the multi-mode type is configured to include a planetary gear set, a plurality of motors/generators which are used as a motor and a generator, a torque delivery device which controls rotating elements of the planetary gear set, a battery which is used as a power source for the motor/generator, and the like.
The transmission system in the multi-mode type has different operation mechanisms depending on a connection configuration of the planetary gear set, the motor/generator, and the torque delivery device. Further, since the transmission system in the multi-mode type has characteristics of which durability, power transmission efficiency, a size, and the like vary depending on the connection configuration, a research and development for implementing a power transmission mechanism which is more robust, reduces power loss, and is compact in a field of the transmission system for a hybrid electric vehicle has continued.
In this view, the brake device of hydraulic pressure operating type applied to the transmission for a hybrid electric vehicle as a friction element has to be provided with complex operation mechanism such as an electronic oil pump (EOP) and a valve body and control process so that power is lost and fuel efficiency is deteriorated by weight and size increase.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.